Add warning about using the latest tag

Also change examples to use major version tags instead of `latest`.

README.org

@@ -14,6 +14,12 @@ The examples in this document use the ~podman~ command. Just swap with the ~dock
 
 * Usage
 
+#+begin_quote
+*IMPORTANT:* It is recommended that you pin the image using the major version tags (ie. =24=, =25=). This way, a manual change is required before updating the service to the next major version. You can use this time to make backups in case something goes wrong.
+
+The =latest= tag always points to the latest version. So it has a higher chance of introducing a breaking change by accident. Only use =latest= if you like living on the edge.
+#+end_quote
+
 To run a container, use either ~podman run~ or define a service in a =compose.yaml= file.
 
 ** Run
@@ -21,7 +27,7 @@ To run a container, use either ~podman run~ or define a service in a =compose.ya
 To run with ~podman run~:
 
 #+begin_src shell
-podman run -v ./bitcoin:/home/bitcoin/.bitcoin -p 8333:8333 code.fosterhangdaan.com/foster/bitcoin-core-container:latest
+podman run -v ./bitcoin:/home/bitcoin/.bitcoin -p 8333:8333 code.fosterhangdaan.com/foster/bitcoin-core-container:25
 #+end_src
 
 ** Compose
@@ -33,7 +39,7 @@ version: "3.8"
 
 services:
   bitcoin-core:
-   image: code.fosterhangdaan.com/foster/bitcoin-core-container:latest
+   image: code.fosterhangdaan.com/foster/bitcoin-core-container:25
    container_name: bitcoin-core
    restart: unless-stopped
    volumes: